Cleaning and descaling process



United States Patent Ofiice 3,297,481 Patented Jan. 10, 1967 3,297,481 CLEANING AND DESCALING PROCESS Kenneth W. Newman, Tarzana, Califi, assignor to Purex Corporation, Ltd., Lakewood, Calif., a corporation of California No Drawing. Filed June 19, 1961, Ser. No. 127,422 7 Claims. (Cl. 134-22) This invention relats to vapor phase cleaning or descaling of surfaces, and is particularly concerned with a process employing a steam laden cleaning or scale removing agent adapted for removal of soil, carbonaceous and leaded deposits, ferrous corrosion and the like, from surfaces, especially the various surfaces of vessels, boilers, piping or other equipment, e.g. jet engine component parts.

In many systems such as for power generation, chemical processing and the like, large vessels, boilers and similar equipment are employed usually in combination with piping and associated equipment, such as valves, pumps, agitators, and the like. Such systems require a substantial amount of maintenance work to keep them clean and substantially free of soils and foreign deposits and scale on their interior surfaces. Also, equipment having complicated internal surfaces are diflicult to maintain clean and free of scale.

Ineffective cleaning and scale removal from the internal surfaces of vessels, piping and associated equipment of such systems has hampered proper operation and maintenance of these systems and causes frequent costly shutdowns in operation.

For purposes of cleaning or descaling the interior of such systems, generally, chemical solutions have been employed. However, in the cleaning or descaling particularly of large systems, that is, for example, those having large vessels, extensive piping and the like, it is frequently impractical to fill vessels and piping with treating solutions. In some cases this is due to the very high volumes of the vessels, and in other cases due to the fact that the configurations are built to carry gases and are not designed to hold the weight of the liquid which would be required to fill the system. Furthermore, the large volumes'of treating liquid which would be required are very difficult to handle after they have become contaminated, and the resulting waste disposal problem often presents a major difiiculty.

It is an object of this invention to provide a process for cleanin or descaling of surfaces, employing a vapor phase medium, particularly steam, as carrier for the active cleaning or agents, and which permits thorough and rapid cleaning or descaling of surfaces, particularly the internal surfaces of equipment having complex surface shapes and configurations.

Another object of the invention is the provision of a process for cleaning or descaling of surfaces, employing a vapor phase medium, particularly steam, as carrier for the active agent or agents, and wherein such active agent or agents are in a form when borne by the steam, such that said agents are essentially inactive, but on condensation of the steam carrier medium said agents are rendered active for cleaning or descaling service.

Yet another object is the provision of a simple, inexpensive process particularly suited tor cleaning or descaling of the interior surfaces of systems, including, for example, relatively large vessels and/or complicated piping, involving the use of relatively small volumes of active agents which accordingly present a minimum disposal problem.

- A still further object is to develop a process of the type noted above which is versatile and permits use of active cleaning or descaling agents which initially may be in solution, powder or even gaseous form. 1

Other objects and advantages of the invention will appear hereinafter.

By the term descaling as employed herein, is meant removal of foreign deposits on surfaces, which deposit-s may be of any type, such as rust, oxides of metals other than iron, such as lead oxides, halides, etc, carbonaceous deposits, and the like.

According to the invention, I disperse an active cleaning or descaling agent in superheated steam, the agent being of a type which is water soluble, forming a steam dispersion, the steam acting as a carrier for the agent. Such steam dispersion is then conducted to the surface to be treated which is maintained at a temperature below the condensation temperature of the steam, and on contact of such steam borne dispersion with such relatively cool surface, the steam condenses, forming a solvent for the active agent. The active agent dissolves in the steam condensate to produce a concentrated active solution capable of efficiently cleaning or descaling the surface with which it is in contact. In a preferred embodiment, the invention involves the carrying of the active agent in aerosol form in steam to the desired surfaces to be treated, and activation of such agent by condensation of the steam and dissolution of said agent in the condensate.

As an important feature of the invention, I utilize dry or superheated steam, so that the descaling or cleaning agent, when initially present in the form of an aqueous solution, can be flash evaporated upon introduction into the superheated steam, and the remaining solids dispersed in discrete particle form in the carrier steam. Under these conditions the active agents or chemicals are carried by the steam in dry aerosol form, and no appreciable chemical action occurs while the active agent is carried in this manner. This permits introduction of the dry or superheated steam aerosol into a complicated form of equipment such as an extended series of insulated pipes in which it is desired to have little or no chemical action take place, such insulated piping being at a temperature such that very little, if any, steam condensation takes place therein. This piping leads to a chamber which it is desired to clean, descale or decontaminate. The walls or surfaces of such chamber can be maintained at a temperature such that the steam condenses on contact with the chamber Walls, thus activating the agent carried by the steam through formation of an aqueous concentrated solution of such agent. The resulting solution is effective for treatment of such surfaces, e.g. to loosen or dissolve soil or scale deposited on the surface.

The pressure and corresponding temperature of the superheated steam can be varied as desired, depending upon the strength characteristics of the equipment being treated and the distance which the steam aerosol is required to travel through the equipment to reach the area being treated and where condensation of the steam is desired to take place. Thus, where the steam aerosol is being employed for treatment of equipment designed and built to withstand high pressures and temperatures, a steam aerosol under high pressure and correspondingly high temperature, e.g. a pressure of 300 lbs. and a temperature of 325 F. can be employed. However, the temperature of the steam is desirably maintained sufliciently low so that rapid condensation of the steam takes place after passage of the steam aerosol through the equipment to the cool area on which the steam is to be condensed to form the concentrated solution of the treat ing agent. I can employ superheated steam at pressures of about to about 250 lbs.

Where the treating, that is, cleaning or descaling agent is initially in the form of an aqueous preferably concentrated solution, such agent can be introduced into the steam by injection through an atomizing spray nozzle, so that the steam, preferably dry or superheated, will cause the water of such solution to flash off, carrying the resulting solid particles of active agent into the steam in dispersed aerosol form. However, instead of atomizing a concentrated aqueous solution of the treating agent into the steam carrier, I can disperse the agent in initially dry powder form, in the preferably dry steam so that the solid particles of active agent are distributed therein in dry aerosol form.

As a further alternative mode of procedure, I may introduce a gaseous type of cleaning or descaling agent into the steam, preferably in dry form, to produce a gaseous mixture wherein the treating agent gas is dispersed in the steam carrier. Under these conditions the gaseous agent is unreactive until the steam condenses on the surface which it is desired to treat, and the gaseous agent dissolves in the water formed from the steam condensate. In this modification I may, for example, employ HF or I-IC gas as, for example, a descaling agent, in suitably small proportions so as to be non-corrosive in the gaseous form, utilizing, if desired, ine-rt diluent gases such as air for this purpose.

Following treatment of a surface by my process, employing the steam-treating agent dispersion or aerosol, to produce the aqueous concentrated solution of the active agent at the locus of treatment, rinsing of the treated surface can be accomplished by means of dry or preferably wet steam; or a water stream, which acts to flush the loosened soil, scale or contaminating material from the treated surfaces or walls, as well as to rinse off any remaining deposits.

The desired resluts according to the invention, can be varied by, for example, varying the ratio of carrier steam to active agent dispersed therein, introducing small amounts of Wet steam into the superheated steam employed as the carrier, so as to produce a dry steam at a lower temperature, varying the amount of active agent employed, and varying the time of exposure of the surface under treatment to the steam-treating agent dispersion. The process can be modified further by treatment of a surface with different treating agents in succession, each preferably in the form of a dry steam aerosol. Thus, for example, in one mode of procedure for cleaning or descaling, a steam aerosol containing an oxidizing type of treating agent such as chromic acid can be employed first, followed by a wet steam rinse, then by a steam aerosol containing a reducing type of treating agent, such as sulfamic acid, followed by a wet steam rinse.

The amount or concentration of treating agent carried by the steam dispersion or aerosol is such that on condensation of the steam, the concentration of treating agent going into solution in the condensate forms a concentrated treating solution. Thus, the amount of the treating agent in the carrier steam can range, for example, from about /2 to about 2 ounces per gallon of feed water from which the steam is produced.

The process of the invention has as major advantages the ability to treat generally inaccessible or complicated internal surfaces or areas, the use of relatively small amounts of treating agents, and the need for disposing of only small amounts of waste. Thus a relatively concentrated solution of the treating agent formed in the process is applied for a relatively short period, and then flushed away by one or more relatively short steam condensations using steam alone.

Examples of treating compositions which can be employed to form the steam dispersions or aerosols according to the invention, are those disclosed in Arden application 511,096 and Arden and Clark applications 511,099, both filed May 25, 1955, now Patent Nos. 2,992,995 and 2,992,997, respectively, and Patent No. 2,843,509. These are basically alkaline compositions containing alkali and an alkanolamine, such as polyalkanolmonoamine and/or alkanolpolyamine, effective for removal of carbonaceous and leaded deposits, and for derusting. Examples of other know derusting agents which can be utilized in the invention process are sulfamic acid and citric acid, and ex- COMPOSITION A Percent by weight Caustic soda 70 Triethanolamine 18 Sodium gluconate 12 Compositions which may be incorporated in steam in the form of a steam dispersion or aerosol for removal of carbonaceous deposits according to the invention, are described in above application Serial No. 511,096 and U. S. Patent No. 2,843,509 of B. Arden. A typical form of such compositions described in said patent which can be incorporated in water to form a concentrated aqueous solution having a concentration of 48 ounces of composition per gallon of solution is noted below:

COMPOSITION B Parts by weight Sodium hydroxide 12 Potassium glycollate 15 Sodium acetate L 12 Triethanolamine 15 The description of the compositions of said copending applications and said patent referred to above are incorporated herein by reference.

The following are examples of operation according to the invention.

Example 1 Into superheated steam at a pressure of lbs. is injected by means of a metering pump an aqueous solution, Composition A above, in a concentration of 1 ounce of Composition A per gallon of feed water used in producing the steam, causing the water in Composition A to flash off, to form a dry steam aerosol carrying the re- ;naining components of Composition A in essentially solid orm.

The resulting steam aerosol is then introduced through the piping of processing system to a vessel connected to said piping, after the piping is first raised to an elevated temperature by prior passage of dry steam through such piping. The interior surface of said vessel, having rust deposits thereon, is maintained at a relatively cool temperature less than 200 F. The steam aerosol passes through'the piping substantially without any steam condensation therein, but on entering the vessel, the relatively cool walls thereof cause the dry steam aerosol to condense on the interior surfaces thereof to form a hot concentrated aqueous solution of the solid components. Such treatment is carried out for a period of about 20 to 60 minutes.

Wet steam is then passed through the system to rinse the interior surface of the treated vessel.

On termination of the above procedure substantially all rust incrustations are removed from the interior surface of the vessel.

Example 2 Composition A in fine powder form is atomized into superheated steam at about 100 lbs. pressure, to form a dry steam aerosol containing about ounces per gallon of feZd water used in forming the steam, of Composition This steam aerosol is introduced into a steel vessel the interior walls of which are coated with rust. The walls of such vessel are maintained at a temperature below the condensing temperature of the steam aerosol, so that on contact thereof with said walls, the steam condenses bringing down the solid particles of Composition A and producing a concentrated aqueous solution in contact with the rust scale on the interior Walls of the vessel. Such treatment is carried out for a period of about to 60 minutes, followed by introduction of a wet steam rinse, and then a hot Water rinse, substantially removing the rust incrustations from the interior surface of the vessel.

Example 3 The above noted concentrated aqueous solution of Composition B is injected into superheated steam at 80 lbs. pressure to form a dry steam aerosol containing about 1% ounces of Composition B per gallon of feed water employed in producing the steam. The resulting steam aerosol is then introduced into a jet engine combustion chamber inner liner having carbonaceous deposits on its interior walls. The walls of the inner liner are maintained at a temperature below 200 F., causing condensation of the steam aerosol on the carbonaceous deposits covering the interior of the liner. Such condensation brings down active agent, that is, the solid particles of Composition B carried by the aerosol, forming a hot concentrated aqueous solution which acts to loosen and wash away such carbonaceous deposit. Such treatment is continued for about 10 to 60 minutes. A- wet stream is then introduced into the inner liner to rinse out the treating solution and any remaining loose carbon deposit.

From the foregoing it is seen that I have developed a process for carrying a water soluble treating agent to its locus of use by carrying such agent in dispersion in steam, preferably in the form of a dry aerosol in superheated steam, and condensing such agent to form directly an aqueous solution of the treating agent at such locus of use. Such process possesses several advantages over the use of aqueous processing solutions, including use of relatively small amounts of treating agents, minimum waste disposal problem, efficient treatment of remote and relatively complicated interior surfaces, and the like.

While I have described particular embodiments of my invention for purposes of illustration, it should be understood that various modifications and adaptations thereof may be made within the spirit of the invention as set forth in the appended claims.

I claim:

1. A process for cleaning of foreign matter from an internal surface of a piece of equipment by means of a water soluble cleaning agent, which comprises dispersing externally of said piece of equipment, said agent in a substantially chemically inactive form in superheated steam, conducting the resulting steam dispersion of said agent in said chemically inactive form to said piece of equipment and interiorly thereof to said surface, condensing said steam dispersion on said surface, and forming a concentrated aqueous solution of said agent in the resulting steam condensate, in contact with said surface.

2. A process for cleaning of foreign matter from an internal surface of a piece of equipment by means of a water soluble cleaning agent, which comprises dispersing externally of said piece of equipment, said agent in the form of discrete solid particles in superheated steam to form a dry steam aerosol with said agent carried in a substantially chemically inactive form in said steam, conducting said steam aerosol to said piece of equipment and interiorly thereof to said surface, maintaining said surface at a temperature below the temperature of condensation of said steam, condensing the steam from said aerosol on said surface and forming a concentrated aqueous solution of said agent in the resulting steam condensate, in contact with said surface.

3. A process for cleaning of foreign matter from an internal surface of a piece of equipment by means of a Water soluble cleaning agent, which comprises injecting at a location externally of said piece of equipment, an aqueous solution of said agent into superheated steam, the amount of said agent employed ranging from about /2 to about 2 ounces per gallon of feed water used in producing said steam, flashing off the water from said aqueous solution and forming a steam aerosol with said agent carried in the form of dispersed fine solids in a substantially chemically inactive form in said steam, conducting said steam aerosol to said piece of equipment, introducing said steam aerosol into said piece of equipment and conducting said steam aerosol to said surface, maintaining said surface at a temperature below the temperature of condensation of said steam, condensing the steam from said aerosol on said surface and forming a concentrated aqueous solution of said agent in the resulting steam condensate, in contact with said surface, and treating said surface with said solution for a period sufficient substantially to remove said foreign matter.

4. A process for cleaning of foreign matter from an internal surface of a piece of equipment by means of a water soluble cleaning agent, which comprises introducing and dispersing at a location externally of said piece of equipment, said agent in fine powder form in superheated steam, and forming a steam aerosol with said agent carried in a substantially chemically inactive form in said steam, conducting said steam aerosol to said piece of equipment, introducing said steam aerosol into said piece of equipment, and conducting said steam aerosol to said surface, maintaining said surface at a temperature below the temperature of condensation of said steam, condensing the steam from said aerosol on said surface and forming a concentrated aqueous solution of said agent in the resulting steam condensate, in contact With said surface.

5. A process for cleaning of foreign matter from the internal surface of a confined zone within a piece of equipment by means of an active water soluble cleaning agent, which comprises injecting at a location externally of said piece of equipment, a concentrated aqueous solution of said agent into superheated steam at a pressure ranging from about to about 250 lbs., the amount of said agent employed ranging from about /2 to about 2 ounces per gallon of feed water used in producing said steam, flashing off the water from said aqueous solution and forming a steam aerosol with said agent carried in the form of dispersed fine solids in a substantially chemically inactive form in said steam, conducting said steam aerosol to said piece of equipment and through a first confined zone therein, maintaining the wall of said first zone at a temperature above the temperature of condensation of said steam substantially to prevent condensation of steam from said aerosol on said Wall, conducting said steam aerosol through a second confined zone remote from the entrance to said first confined zone, maintaining the Wall of said second zone at a temperature below the temperature of condensation of said steam, condensing the steam from said aerosol on the internal surface of said last mentioned wall and forming a concentrated aqueous solution of said agent in the resulting steam condensate, in contact with the wall of said second zone having said foreign matter on the surface thereof, and treating said surface with said solution for a period sufiicient substantially to remove said foreign matter.

6. A process for removal of a deposit selected from the group consisting of carbonaceous, rust and leaded deposit from an internal surface of a piece of equipment by means of a Water soluble cleaning agent in the form of a composition containing alkali and an alkanolamine, which comprises dispersing externally of said piece of equipment, said agent in the form of fine solids in superheated steam to form a dry steam aerosol with said agent arried in a substantially chemically inactive form in said team, conducting said steam aerosol to said piece of quipment and interiorly thereof to said surface, mainaining said surface at a temperature below the temperture of condensation of said steam, condensing the steam rom said aerosol on said surface and forming a conentrated aqueous solution of said agent in the resulting team condensate, in contact with said surface.

7. A process for removal of a deposit selected from he group consisting of carbonaceous, rust and leaded leposit from the internal surface of a piece of equipment )y means of a Water soluble cleaning agent, which comarises dispersing externally of said piece of equipment, aid agent in the form of fine solids in a substantially :hernically inactive form in superheated steam, conductng said steam dispersion of said agent in chemically inactive form through a piping system to the interior of said niece of equipment, maintaining the walls of said piping :ystem at a temperature above the temperature of coniensation of said steam substantially to prevent condensa- ;ion of steam from said dispersion on said walls, main- :aining said surface at a temperature below the tempera- :ure of condensation of said steam, and condensing the steam from said dispersion on said surface and forming a concentrated aqueous solution of said agent in the resulting steam condensate, in contact with said surface.

References Cited by the Examiner UNITED STATES PATENTS Barnard et a1. 134-35 Cleveland 134-29 Cleveland 13429 Vollrath 13441 X Szodomka.

Cricker 13436 X Todd 87 -5 Dinley 87-5 Parker et a1. 134-27 X Petering et a1. 134-31 Gelles et a1. 134-36 X Arden 13439 Loucks 134-22 FOREIGN PATENTS Great Britain.

4/ 1940 Great Britain.

MORRIS O. WOLK, Primary Examiner.

CHARLES A. WILLMUTH, DONALL H.

SYLVESTER, Examiners.

I. T. ZATARGA, Assistant Examiner. 

1. A PROCESS OF CLEANING OF FOREIGN MATTER FROM AN INTERNAL SURFACE OF A PIECE OF EQUIPMENT BY MEANS OF A WATER SOLUBLE CLEANING AGENT, WHICH COMPRISES DISPERSING EXTERNALLY OF SAID PIECE OF EQUIPMENT, SAID AGENT IN A SUBSTANTIALLY CHEMICALLY INACTIVE FORM IN SUPERHEATED STEAM, CONDUCTING THE RESULTING STREAM DISPERSION OF SAID AGENT IN SAID CHEMICALLY INACTIVE FOR TO SAID PIECE OF EQUIPMENT AND INTERIORLY THEREOF TO SAID SURFACE, CONDENSING SAID STREAM DISPERSION ON SAID SURFACE, AND FORMING A CONCENTRATED AQUEOUS SOLUTION OF SAID AGENT IN THE RESULTING STREAM CONDENSATE, IN CONTACT WITH SAID SURFACE. 